The class of polymers of carbon monoxide and olefin(s) has been known for a number of years. Early processes for the production of such polymers were typically free radical processes as illustrated by Brubaker, U.S. Pat. No. 2,495,286. The polymeric products of such processes were typically relatively low in carbon monoxide content.
More recently, processes for the production of polymers of carbon monoxide and ethylenically unsaturated hydrocarbon have been developed wherein the polymer product is a linear alternating polymer of carbon monoxide and ethylenically unsaturated hydrocarbon. Such processes typically employ a Group VIII transition metal compound or complex as catalyst. A recently developed process which is becoming of greater interest is described in published European Patent Applications 121,965 and 181,014. These processes employ a catalyst composition formed from a Group VIII metal salt wherein the metal is palladium, cobalt or nickel, the anion of certain strong acids and a bidentate ligand of phosphorus, arsenic or antimony. During the polymerization, the polymers are obtained in the form of a suspension in a diluent. The preparation of the polymers can, in principle, be carried out in either of two manners, viz. batchwise or continuously.
Batch preparation of the polymers is carried out by introducing the catalyst into a batch reactor containing the diluent and the monomers and which is at the desired temperature and pressure. As polymerization proceeds, the pressure drops, the concentration of the polymers in the diluent increases and the viscosity of the suspension rises. Polymerization is continued until the viscosity of the suspension rises. Polymerization is continued until the viscosity of the suspension has reached such a high value that continuing the process further would create difficulties in connection with heat removal. In principle, the only parameter which remains constant in batchwise polymer preparation is the temperature. A variant of batch polymerization is semi-batch preparation in which besides the temperature also the pressure is kept constant by adding monomers to the reactor during the polymerization.
In continuous polymer preparation, the diluent, the monomers and the catalyst are added to a reactor and a polymer suspension is continuously withdrawn from it. During the continuous polymer preparation, the temperature, the pressure and the liquid volume in the reactor are kept constant. After a starting-up period in which the polymer concentration in the suspension increases to the desired value, a stationary state is reached which is characterized by the suspension withdrawn from the reactor having a constant polymer content and the polymers contained therein having a constant bulk density.
For the preparation of the polymers on an industrial scale, a continuous process is greatly to be preferred to batchwise or semi-batchwise production for the following reasons. In the first place, the continuous process gives a higher polymer output because production does not, as in batch preparation, have to be frequently interrupted for charging and discharging the reactor. Since continuous operation, in contrast with batch production, is characterized by all the reaction parameters remaining constant, a continuous process is easier to regulate and is more suitable for automation. Finally, the continuous process produces polymers which exhibit less variation in properties and therefore have a more constant quality than those obtained from batch production.
Linear alternating polymers of carbon monoxide and olefinically unsaturated compounds have previously been made by batch processes which typically produce polymers having bulk densities less than 3 g/ml. Bulk density plays an important role, both in the preparation and also in the refining, storage, transport and processing of the polymers.
As regards the preparation of the polymers, it can be stated in approximate terms that the maximum permissible suspension concentration, expressed in kg polymer/kg suspension, is about one hundred times the bulk density expressed in g/ml. This means that when preparing a polymer with a bulk density of 0.1 g/ml, the maximum suspension concentration will be about 10% and when preparing a polymer with a bulk density of 0.5 g/ml the maximum suspension concentration will be about 50%. Thus, increasing the bulk density by a factor of five enables about five times as much polymer to be prepared in the same reaction volume.
As regards the purification of the polymers, such as filtering, washing and drying, the quantity of attached liquid is determined to a large extent by the bulk density of the polymers. It has been found, for example, that a polymer with a bulk density of 0.1 g/ml binds about 5 g diluent or washing liquid per gram, while the corresponding quantity for a polymer with a bulk density of 0.5 g/ml is only 0.25 g. This is naturally very important in connection with the quantity of liquid needed for washing the polymers and that subsequently has to be removed when drying the polymers.
As regards transport and storage, the polymers exhibit a more attractive flow behavior and occupy less space the higher their bulk density.
As regards processing, polymers with a low bulk density must often first be compressed, for example by extrusion, in order to make them suitable for further processing in the customary apparatus. The extrusion of polymers always changes the polymer to some extent by inducing crosslinking, chain scission, or further polymerization. The higher the bulk density of the polymers, the less need there is for a pretreatment of the material, which is thus suitable for further processing.